This invention relates generally to a flight safety system, and more particularly to an improved method for computing driftdown plans for use by commercial, private or military aircraft flight personal.
Government aircraft regulations require that commercial airlines, using multi-engine aircraft, have available for immediate emergency use, a plan whereby, upon loss of an engine anywhere along a planned route, altnernate landing sites, other than the planned destination, are specified where the loss in altitude due to engine failure (driftdown) will not result in the aircraft dropping below a minimum safe elevation relative to the earth's surface as it exists in the route of travel. In the past, it has been the practice of the airlines to manually generate a so-called driftdown plan using data supplied by the aircraft manufacturer relating to the aircraft's performance. Typically, based upon the information contained in so-called "burn tables" and "driftdown curve tables" for each manufacturer's engine type and with the aid of a terrian elevation map, a driftdown plan was prepared for each leg of an authorized route.
This rather time consuming process has proven to be much less than satisfactory in that it does not properly take into account certain real-time parameters which could effect the results of the determination as to whether a planned alternate landing site, would, in fact, be acceptable. For example, wind and weather conditions cannot accurately be predicted much in advance of a scheduled departure time. As a result, driftdown plans which may be prepared many months in advance of any expected use and which are maintained in a manual on board the aircraft, ignored such conditions. Thus, to ensure safety irrespective of weather or wind or other variable conditions, the prior art driftdown plans imposed stringent limitations on load factors such that the airlines have been unable to effectively utilize the seating capacity of the aircraft. This, of course results in a loss in passenger revenues.
Occasions also arise where, depending upon how much air traffic is around, a FAA Flight Controller may direct a course between a city of origin and a destination which is different from the airline's usual route between those cities. When a different route is involved, personal on board the aircraft may not have available in its canned set of driftdown plans a plan which would cover this alternate course. Furthermore, unscheduled flights, such as charter flights, may be routed from an origin to a destination so as to cover a flight path for which the charter airline may not have previously generated or obtained a driftdown plan. Then too, whenever a commercial airline desires to get a new route approved, the airline must provide the FAA with detailed driftdown plans, which plans, of course, must be revised to the extent that the FAA specifies the routing which may differ that being requested. The need to prepare and revise the driftdown plans using manual methods is not only time consuming but costly as well.
The system of the present invention obviates, for the most part, all of the drawbacks and disadvantages of the prior art methods alluded to above. Employing a general purpose digital computer containing an appropriate data base and programmed in a fashion set forth in detail hereinbelow, persons desiring a driftdown plan can obtain same in a matter of moments, the plan taking into account standard and nonstandard routes, weather conditions, traffic loads, etc. Knowing a planned flight path in terms of the latitude and longitude of the vectoring points along the route, and knowing the fuel on board, the altitude at the top of climb point, the weight of the aircraft at the top of climb, and by combining these data with "worst case" international standard atmospheric (ISA) temperatures and aircraft/engine "worst case" bleed air configurations, the computer is able to project whether an aircraft, losing an engine would be able to drift down to its planned destination while still clearing all terrain on 10 miles either side of the flight path by at least 2000 feet. Where it is determined that the aircraft cannot sustain a sufficiently high altitude to clear all terrian by 2000 feet vertically in attempting to reach its scheduled destination upon the loss of an engine, the computerized system of the present invention will automatically determine what alternate landing sites would be available. The alternate sites may either be automatically determined by the computer or the operator may propose an alternate site and have the system of the present invention determine whether that site is a viable alternative. In either instance, the test is whether there is any limiting terrian within ten miles of either side of the flight path leading to that alternate desitnation. Also, at the time that an alternate is designated, wind conditions, (both velocity and direction), remaining fuel and other factors are taken into account in determining the ability of the aircraft to reach that alternative landing site should an engine fail.
The computer system of the present invention operates on an iterative cycle at predetermined increments of distance along the flight path, typically every 10 miles. That is to say, at 10 mile increments along the scheduled route a determination is made whether the aircraft could drift down, upon the loss of an engine, to its planned destination and if not, whether it can make it back to its origin or to some other operators specified or computed alternate landing site. In addition, the system of the present invention provides a printout at each decision point of its longitude and latitude, the weight of the aircraft, the amount of fuel remaining, the distance and heading to the alternate and the approximate altitude that the aircraft will be at the alternate, considering the driftdown accompanying the loss of an engine.